I have a 320 slim (not super slim) and that is lovely and QT, until it reads the disc, then it is loud.
I have had 4/5 (can't remember!) ps3's from the original fat badboy (I liked those) to my current white 320gb and they have all been very loud when rerading from the gamedisc, otherwise lovely and quiet.
...Just don't play MW3 onit, now that was a fucking joke, the disc reading noise, not the game... Have a look on youtube and see.

My 80 gig phat was very quiet. Now my 120 gig Slim is my main console and its quiet, but not as much as the other machine. Also got a first gen 120 gig Slim which is horrible as the constant whine is so off putting.

I've owned an 80Gb phat (August 2008), a 250Gb Slimline (Oct 2009) and a 320Gb Slimline (April 2011) and the 250Gb Slimline was definitely the quietest, especially at reading discs and powering down the fans.

Sony most have changed component suppliers when they went from the 120Gb/250Gb models to the 160Gb/320Gb ones as the fans in the former power down gracefully and slow down, the latter just stop abruptly; you can hear the hard drive head parking up against the edge of the unit in the latter units, not the former; most importantly the optical drive in latter units are really noisy compared to the former, especially for certain open world titles like Red Dead or Just Cause 2, my thing practically sounds like a typewriter playing one of them, and has done out of the box. My old 250Gb was lovely and quiet in that regard.

I did have some doubts about the latest model, because it generally looks somewhat cheap and rattly to me. I still have my original 80GB fat, which is pretty silent except for the BD drive, which can make loading a bit noisy.

Nice to hear the original Slim was best, since I also think it's the best-looking one.

Get a slim.. they're super quiet until they get hot but to be fair whichever game pushes the CPU/GPU to it's max (the last of us example) will make any of them a little nosier. The slim can be had cheap and it's damn reliable.

My launch 60GB sounded like a haridryer on full meaning it couldn't be left on, to watch a bit of tele, as the noise was so bad I had to turn the amp up a good 5/6 points to make up for it. Ofcourse it then went and died on sunday, which may be part of the reason it sounded like a traction engine. I'm picking up a superslim to replace it - only just managed to get the last of us out the drive using the old hairdryer/towel trick. Hope the SSlim is at least a bit quieter.

My launch 60GB has become very loud lately. I'm guessing it must be really dusty inside. I think I'll open it up during the weekend to clean it out.

I'm saying this because any type of high-power device which requires constant cooling will get clogged with dust as time goes by and really should be cleaned after some years, preferably after the warranty has run out, and by someone at least a little experienced in taking electronic stuff apart.

Unless you have an "I void warranties" t-shirt from ThinkGeek, like I do. Then you can open anything, any time.

But seriously, just like with a PC when you simply have to open it up every now and then to take the fistfuls of dust out, so should you any other device with high airflow. They don't make it easy, though, do they.